The design and synthesis of bioinspired materials such as synthetic light harvesting complexes, artificial ion channels, artificial muscles, has captured the imagination of many individual research groups. Very few efforts, however, have been directed toward the full integration of biologic and synthetic materials for the creation of hybrid biofunctional devices. Accomplishments in the area of bacteriorhodopsin-based optoelectronic devices (Birge, IEEE Comput. 25, 56 (1992)), gramicidin-based biosensors (Cornell et al., Nature 387, 580-583 (1997)), and photochemical triad-driven ATP synthase processes (Steinberg-Yfrach et al., Nature 392, 479-482 (1998)) constitute important advances that have involved multidisciplinary investigative groups to direct the design, synthesis, processing, structural analysis, and performance testing of these devices.
It has been 20 years since the first demonstration that Langmuir-Blodgett films could be used to assemble lipid bilayers on solid surfaces (Von Tschamer et al., Biophys. J. 36(2), 421-427 (1981)). This initial work inspired intense interest in biotechnologies based on supported lipid bilayers because of the important role that membrane proteins play in living systems. Unfortunately, applications of supported lipid membranes have been limited by their instability. Recent breakthroughs by Cornell et al (Nature, 1997, 387:580) and Bieri et al. (Nature Biotechnol., 1999, 17:1105) in anchoring chemistries and protein orientation, respectively, have produced durable asymmetric biofunctional membranes Channel proteins are embedded in the membranes to provide biofunctionality. Cornell et al. describe the incorporation of gramicidin dimers in membranes formed from a tethered lipid bilayer. Bieri et al. describe the use of conventional bilayers with the G-protein coupled receptor, bacteriorhodopsin. This protein is oriented with respect to the surface using a streptavidin-biotin interaction. Others have used a silyl-modified polyethylene glycol (PEG) to tether a supported membrane to glass.
Despite these advances, the stability of planar membrane structures remains an issue. Moreover, conventional methods are limited to the use of channel proteins and require chemical modification of the protein that is often non-specific or difficult to control. Biofunctional membranes exhibiting increased stability and/or broader utility are needed in order to meet the complex needs of nanotechnology and biotechnology.